The present invention relates to a fluid motor driven pump arrangement having motive fluid exhaust in the pump chamber.
Danish Patent No. 155656 discloses a mixing plant for mixing one component, for example lubricating oil, with another component, for example gasoline, which drives a piston type liquid motor which in turn drives a crank shaft on which is mounted a rotating valve. This controls delivery and discharge of the drive medium to two pistons in the liquid motor, and an impulse generator coupled to an electronic counting device.
To one of the pistons or to both pistons, there is coupled a piston in a dosing pump by means of a compressible connection rod. The stroke of the piston in the dosing pump, and consequently the performance of the pump, can be varied by means of an adjustable stop or a stop screw mounted in the top of the cylinder in the dosing pump.
The said known mixing plant does not seem to comprise means to prevent the liquid motor from stopping in an extreme position. This might be overcome with a flywheel, but there will still remain the problem of starting the motor from such extreme position. Furthermore, the shown rotating valve must have the effect that, during the change-over operation, a slow-down in the speed of the closing for flow of liquid to and from the cylinders will occur before there is a free flow again. This produces an uneven delivery and discharge of liquid, possibly with harmful liquid-hammer blows. Adjustment of the dosing operation by means of an adjustable stop screw is not well suited if the dosing pump is to operate with high as well as low pressures. Furthermore, the known system will give a periodic delivery of the liquid medium which is to be dosed.
Furthermore, mixing plants are known in which a liquid medium A is dosed into another liquid B which flows through a pipe, and in which the volume of flow of liquid B is metered by a flowmeter. This could, for instance, consist of a turbine wheel giving electric impulses in relation to the volume of flow through the pipe. Other metering methods consist of a magnetic field being laid over the flowing liquid or sending ultrasonic signals through the liquid.
But it does not always happen that the electrical conductivity or the sound-dampening character of the liquid medium permits the use of electro-magnetic flowmeters or ultrasonic flowmeters.
The liquid flow is converted to an electrical signal which is an input signal to an electronic circuit whose output signal is used to control an electrically driven dosing pump, which could be an electric motor or a solenoid coil, which moves a piston or a diaphragm in the pump.
The dosing accuracy is determined by the accuracy of the flowmeter. Many types of flowmeters do not, neither in theory nor in practice, live up to a linear relation between volume flow and signal emitted. If an accurate metering is needed, it will be necessary to use flowmeters which are relatively expensive.
These systems consist of several components, which have to be connected electrically or hydraulically to each other, and it will be necessary to have one or more electrical voltage supplies. It is a great drawback to have electrical components in a plant with flowing aggressive chemicals or strong electrolytes, which easily penetrate electrical components and cause corrosion and short circuiting in the live components.